ch25_review - If I know the focal length in meters, the...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
A. Manalaysay – PHY2054, Fall 2004 CHAPTER 25 First of all, read sections 25.2 and 25.3 (do it right now… put this paper down). So now you’ve read those sections, let’s review. All this stuff uses concepts already learned in chapter 23. Farsightedness: it means you can’t focus on anything closer than a certain point, called your “near point”. Nearsightedness: it means you can’t focus on anything farther than a certain point, called your “far point”. The way you need to think about glasses is this: if someone who is farsighted wants to see something that’s closer than their near point, we consider this thing the object distance (p) and their near point the image distance (q). The same holds for people who are nearsighted, except the far point is now the image distance (q). Once we know p and q, we can find the focal length of the lens (i.e. glasses or contacts).
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: If I know the focal length in meters, the power of the lens is 1/f , in units of diopters. This can be positive or negative. Simple magnifier (i.e. a magnifying glass): Theres not much to this section that you havent already learned in chapter 23. The only new concept here is that of angular magnification. What you have to realize is that when you look at an object, you see that it has a certain size, but in actual fact, your eye just sees that the object is a certain angle wide (because your eye only knows direction). Look at figure 25.5 on page 787 if this last sentence confuses you. Clearly, if I change the apparent size of an object, the angle it takes up when you look at it will change. So, the angular magnification is given by: m = / , where is the angle spanned by the image and is the angle spanned by the object. THE END. GOOD LUCK!...
View Full Document

Ask a homework question - tutors are online